Sound-reproducing system



Apri! 21, 1931.

D. A. WHITSON 1,801,472

SOUND REPRODUCING SYSTEM Filed July 50, 1928 2 Sheets-Sheet 1,qr-rozlvsy April 21, 1931. D. A. WHITSON SOUND REPRODUCING SYSTEM FiledJuly 30, 1928 2 Sheets-Sheet 2 erraervsy 1 15 commonly usedloud sPatented Apr. 21, 1931 UNTTED STATES PATENT? OFFICE DELMLAB WHITSON, LOSANGEIOES, CALIFORNIA, ASSIGNOB TO WHI'ISON PHOTO- PHONEOORPOBATION, OFLOS ANGELES, CALIFORNIA, A CORPORATION OF NEVADA BOUND-BEPBODUGINGSYSTEM Application filed. July 80,

This invention relates to sound reproduction, and especially toreproduction from photo aphic records. A

uch records are now "well known. In on form, for example, the record isproduced on g a film, the density (or degree of translucency islongitudinally variable in accordance wit the sound to be reproduced.Now if such a record he passed between a steady source of light and aphoto-electric device, this device can control the current in a circuit,and-the resultant current variations can be caused to operate a devicethattranslates cur-rent variations into sound; such for exam le as thenow akers. ince such reproducing systems as ust outlined are now inquite general use, and especially in connection with talking movies, itis considered unnecessary to detail them further.

My invention is in the nature of an improvement over a system of thischaracter; and accordingly it is one of the objects of my invention toimprove the reproduction of sound by this means.

It is obvious that in a record of this character (the so-called variabledensity record), the record carrying medium should, for perfect results,have its density continuously and accurately variable along its length;in other. words, for each increment of length theremust be acorresponding increment or decrement of density.Practicalconsidemtions'iminediately show that the length incrementscannot be reduced to a mathematical infinitesimal, such as are treatedfor example in differential calculus; and consequently, this theoreticalperfection is lost.

Nevertheless, the human ear being itself incapable of discriminatingbetween perfection and near perfection, highly satisfactory results canbe obtained when the density variations occur in widths of say of theorder of one or two thousandths of an inch where the rectilinear speedof the record is approximately fifteen inches per second at any givenpoint. Consequently when such a density rec 0rd is viewed with the nakedeyes, it appears as a series of very closely spaced bars of vary ingwidths and of varying darkness or density. These bars are the result ofpassing the 1928. Serial No. 298,298.

light that produces the record through a correspondin'gly narrow slit oriris onto the recorddwhich is later photographically develope Forreproduction purposes, the density of each individual bar shouldtheoretically be caused to affect in succession, the photo-electricdevice, so that the device may faithfully follow the density variationsof the whole record. In order to accomplish this result, it has beencustomary to provide a narrow slit or iris across which the record ispassed. However, -1t was found that dirt or other foreign matter soonclogged up at least a portion of the opening, and interfered with thetransmission of light therethrough. Even if the reproduction were notentirely lost, yet due to the irregular blurrin of the optical pathoccasioned by the foreign matter, a serious distort1on would result.Consequently it has been proposed to fill'the slot with a transparent'plug, such as a crystal or glass, that would eifectively keep out theforeign matter.

Such an arrangement is nevertheless far from ideal. The film, travellingin contact with the iris, is rubbed thereb and a scratching of therecord is caused by fine dust or particles trapped between the film andthe slot. It is another object of my invention to obviate all thesedisadvantages and yet secure the highly desirable accurate reproduction.

I accomplish this result by passing the light through an iris that iscomparatively wide; of the order of an eighth of an inch, and bymaintaining the film record entirel out 0 contact with the structure inwhich the opening is rovided. The image of a lar e number 0? striationsor density lines is t en projected in magnified form onto a baflle,which has a slot or an elongated transparent window just wide enough topass only a very small fraction of a single striation onto thephoto-electric device. Since the ima e is optically projected andfractionate by a slot or light passage remote from the film, the slotcan be kept easily free of interfering foreign matter, and may beprovided with a transparent coverin such as a glass plate or plates onboth sides thereby Insuring a clear light path at all times.

The advantages of such an optical system are important. In priordevices, the photoelectric device was subjected at frequent points onthe record to the light intensity roduced by a small group of densitylines, own as harmonic groups, the combined or total width of which wasmuch smaller than the width of the fractionating slot; and accordingly,attempts to record and reproduce variations in tone volume could not bereadily accomplished, for the individual density variations were lost.In my scheme the tone volume can readily be recorded and reproduced, fora very much finer subdivision of the'lines is provided, and the densityvariations, which occur over the entire width of the individual linesbeing the volume factor, can be reproduced by making the magnificationsufiiciently large, and the opening or window in the baflie platesuificient narrow, so as to scan across the width of the line from oneedge to the other. Such scannin is practicall impossible where a slothaving a width 0 .001 of an inch is directly employed to fractionatefundamental tone lines more or less of that width, and harmonic linesare present possibly as narrow as .0005 or even .0002 of an inch, whichcondition now obtains in other devices for reproducing sound.

'My invention possesses many other advantages, and has other objectswhich may be made more easily apparent from a considera tion of oneembodiment of my invention. For this purpose I have shown a form in thedrawings accompanying and forming part of the present specification. Ishall now roceed to describe this form in detail, which illustrates thegeneral principles of my invention but it is to be understood that thisdetailed description is not-to be taken in a limitin sense, since thescope of my invention is Eest defined by the appended claim.

Referring to the drawings:

Figure 1 is a diagrammatic view of a reproducing system incorporating myinvention; the optical system and its associated structure being shownmainly in section.

Fig. 2 is a side elevation of the optical system and its associatedstructure, some of t 0 parts being broken away to illustrate thestructure more clearly.

Fig. 3 is a plan view thereof; and

Fig. 4 is a diagram of a ortion of the ma ified image with the batleplate.

ig. 5 is a magnified view of an individual tone line or photographshowing the density variation, or graduation over its entire width,characteristic of the volume factor.

The record film 11 in this instance is shown as carrying not only thesound record 12, but also the frames 13 of a motion picture for thepurpose of producing talking pictures. This film has a series of srocket tooth engaging apertures linear 021(1 edge;

. adjacent support 28, can

in the present instance, only the apertures at the right hand edge (Fig.3) are engaged by a sprocket wheel 15. This wheel as most clearly shownin Fig. 1, can be used as a driven wheel, as by the provision of a driveshaft 16. Optionally one or the other sprocket wheels 17 (Fig. 2) can beused as a driver; otherwise it can serve, as sprocket 18, merel as atensionin idler. Other idlers, suc as 19, 20, 21, canie used to maintainthe film 11 in proper arcuate configuration with respect to wheel 15.

\Vheel 15, as shown in Fig. 2, is provided with an undercut flan e 22that is of considerably less width than film 11, so that the free edgeof the film projects beyond the narrow rim 23 and is supported thereon.The film 11 is urged sidewise to maintain it in correct position withrelation to the optical system, as by a ring 24, urged resiliently as bya series of springs 25, against that edge of the film which is nearestthe sprocket wheel. To adjust the spring pressure, an adjustable rin 26is used, against which the springs 25 a ut, and which is adjustable byhaving it threaded onto the screw threads 27 shown as formed as anextension of wheel 15. Wheel 15 has sufficient weight to produce afly-wheel effect, and to maintain the speed thereof substantiallyuniform. This uniformity is quite essential for accurate reproduction.

That part of film 11 which projects beyond rim 23 carries the soundrecord. The optical system whereby light shines through the record willnow be described. A stationary support 28 is used, that has an offsetportion 29 extending beneath flange 23. This portion has an arcuatesegment 30 in which is formed a comparatively wide slot 31 to permit liht to shine through the projecting edge of lm 11 as it travels past.This slot, as shown in Fig. 2, can be stepped in order to preventdifl'raction at the inner edge; and it is furthermore so wide as topreclude the possibility of it clogging. In fact, glass windows canreadily be placed on each end of the slot if necessary.

As shown most clearly in Fi 1, the film 11 is spaced from the slotopening, so that it cannot be scratched or injured by the slot edges.Light can be passed through the slotin any desired manner; for example,an in candescent lamp 32, appropriately supported be used. A lens 33concentrates the light onto a prism reflector 34 supported in the offsetportion 29 of support 28. Lens 35 in this offset portion thenconcentrates the rays to pass it through aperture or slot 31. After thelight passes through film 11, the image of the record thereon ismagnified by anyl desired arrangement, as by lens 36, and t e magnifiedimage is proj ected onto a baflie plate 37 As shown most clearly in Fig.1, the image of the record covering slot 31 at any instant image isallowed to affect the light sensitive device 40, such as aphoto-electric cell. For

this urpose, bafile 37 has a central slot 41, or s win ow wide enough topass only such rays as correspond to a portion only of a density line.These rays can then be again diverged to affect the electronemitting'electrode 42. This device can then be used to afl'ect, in awell known manner, one or more stages of electronic emission amplifierssuch as 43, and finally the amplified electrical im ulses can pass to aloud speaker 44 or equiva ent device that translates these impulses intosound waves. 7

The baflle plate 37 is shown as having an exaggerated slot opening 44.As a matter of fact, the slot is made very narrow, as indicated by theline 45 in Fig. 4, so that it serves to fractionate or scan theindividual bars. In this way, the variations in volume of the sounds orinally recorded can be faithfully reproducetf The slot in bafile plate 37may be equipped with transparent windows, such as a sheet of glass ormica, cemented on either or both sides of the battle as shown at 37a,thereby preventing the accumulation of dirt or foreign matter in thelight passage, or the baflle plate may be made of a transparent solidsuch as glass or quartz coated or covered on one face with an opaquesubstance, that is heavily silvered or painted and a very narrow lineruled through the covering to the glass surface thereby permittin lightto pass, as if it were an open slot. T 's arrangement permits easycleaning when, if ever, any dirt should accidentally accumulate at thatpoint. In view of the fact that the bafile plate is remote from theaccumulated dirt adhering to the film, this elementary trouble isentirely overcome.

I claim:

In a structure defining a slot for photo- I graphic sound records, awheel over which the record can be placed, said wheel having a flangebeyond which the record can project, a stationary support having a partprojecting beneath said record, and forming wlth the wheel an openingover which the record travels, a lens structure arranged to passradiations radially through the opening, and supported on said part, anda reflector also supported thereon, for directing radiations from asource through the lens.

In testimony whereof I have hereunto set in hand.

y DELMAR A. WHITSON.

